An internal combustion engine is known where efficiency of a crank movement of a crank chain is improved by reducing friction due to a side pressure applied to a piston from an inner wall of a cylinder bore. In particular, a structure is known where the side pressure to the inner wall of the cylinder bore applied to the piston is reduced by employing a two-piece connecting rod including first and second connecting rods and a guide member at a joint portion thereof, and a rolling member provided at the guide member is brought into rolling contact with the inner wall of the cylinder bore to reduce the side pressure applied to the inner wall of the cylinder bore, which is applied in turn to the piston. For example, see Japanese Utility Model Application No. 60-63357 (JP-UM-A-61-179341) and JP-A-8-303254.
In JP-UM-A-61-179341 and JP-A-8-303254, and with reference to FIGS. 8 and 9, crank chains in engines are each provided with a two-piece connecting rod 02 having first and second connecting rods 021, 022. The first connecting rod 021 is connected at one end 021a thereof to a crankpin 01a of a crankshaft 01 and is connected at the other end 021b thereof to a sliding member 0P2 provided with a rolling member 0P21, such as a roller bearing or a wheel, to be guided by an inner wall of a cylinder bore 020a in contact thereto. The second connecting rod 022 is connected at one end 022a thereof to the sliding member 0P2 and is mounted to and holds a piston (slide runner) 0P1 at the other end 022b thereof. As a result, a structure provided with the connecting rod 02 as a single member including the first connecting rod 021 and the second connecting rod 022 connected to each other via the sliding member 0P2 is achieved.
The crank chain is adapted to reduce friction by receiving a side pressure applied to the inner wall of the cylinder bore 020a due to the operation of the first connecting rod 021 at the time of a crank movement by the sliding member 0P2 provided with the rolling member 0P21 (such as the smoothly rotating roller bearing or the wheel) and reducing the side pressure to the inner wall of the cylinder bore 020a received by the piston 0P1 mounted to the second connecting rod 022, so that energy loss due to friction or the like during the crank movement is reduced by smoothing the reciprocal sliding movement between the piston 0P1 and the inner wall of the cylinder bore 020a, whereby improvement of efficiency of the engine is achieved.
In JP-UM-A-61-179341 and JP-A-8-303254, the crank chains are each provided with the two-piece piston connecting rod including the first and second connecting rods as described above, and structurally, a distance between a crank web portion and the piston is relatively long, and hence the first connecting rod is relatively long.
Regarding a behavior of the piston in the crank chain, a long connecting rod connecting the crankpin and piston is not suitable for increasing the speed of the piston, in particular the behavior of the piston near a top dead center.
Delay of the piston behavior leads to thermal energy loss by an amount corresponding to an excessive time due to the delay of the piston behavior. In particular, in a quick combustion engine which requires a quick piston behavior, the engine structure in which the length of the piston connecting rod is long as described above can hardly be employed.
Therefore, a crank chain in which a quick piston behavior near the top dead center of the piston is achieved during the crank movement is required.